The invention relates to a method for supplying fuel to a combustion engine which has an air inlet provided with a gas valve and an output shaft and wherein a fuel line in which a fuel supply device is arranged debauches into the air inlet, comprising of providing a pump with an adjustable, substantially continuous flow rate for the fuel supply device, determining the position of the gas valve, determining the rotation speed of the shaft, ascertaining the required fuel flow rate and adjusting the pump accordingly.
A method of this kind is known from U.S. Pat. No. 4,048,964. The main control signal for adjusting the pump is obtained from a volumetric air flow meter. The derived signal is further adjusted with signals representing the position of the gas valve and the rotational speed of the motor shaft, amongst other signals.
Due to the delay of the air flow meter, the control of the combustion engine has a considerable time constant, at first affecting the accurate control of the fuel supply.
The invention now has for its object to provide a method for supplying fuel which enables very rapid control such that this is suitable for fast-running engines, such as two-stroke racing engines which can have a rotation speed of up to 18,000 rpm.
This object is achieved with the method according to the invention in that the required fuel flow rate is ascertained with the determined position of the gas valve and the determined rotation speed of the shaft. Both the gas valve position and the rotation speed can be determined with a very small time constant.
The required fuel flow rate can be calculated for instance with a suitable algorithm. Preferably however, the required fuel flow rate is determined on the basis of a pre-configured matrix in which various gas valve positions and shaft rotation speeds are related to an associated fuel flow rate suitable for a desired operating mode of the engine. A high processing speed can be hereby achieved.
The matrix can be configured by calculation. The matrix is preferably at least partially configured by including therein values wherein the oxygen content of exhaust gases determined with a lambda probe arranged in an outlet of the engine has an optimal value. It is of course also possible herein to use a self-learning method, wherein the values stored in the matrix are gradually optimized during operation of the engine on the basis of simultaneously performed measurements with the lambda probe.
A further refinement of the method according to the invention is achieved by determining at least one parameter, such as the absolute pressure of air flowing through the air inlet, and correcting the determined fuel flow rate accordingly. As for instance the air pressure, air temperature and air humidity vary, modified fuel flow rates can be provided so that a desired optimum operation is obtained under all operating conditions.
The step of determining a rate of change of the shaft rotation speed and adjusting the fuel flow rate based on that rate of change, for a predetermined time duration, is preferably applied particularly in the case of fast-running engines such as racing engines. Due to the "predictive" control a time constant for the control practically equal to zero can be realized. The combustion engine will thus herein obtain the optimum fuel supply at virtually any given moment, both during constant and greatly varying operating conditions.
The invention likewise relates to and provides a combustion engine comprising at least one cylinder, a reciprocally moveable piston therein which can drive an output shaft via a transmission, an air inlet which is connected to the cylinder and in which is arranged a gas valve, fuel supply means debauching into the air inlet and comprising a pump with an adjustable, substantially continuous flow rate, control means for controlling the pump, sensors connected to the control means for at least the shaft rotation speed and the gas valve position, wherein the control means are programmed such that they control the pump in the manner as described above.
Preferably, the air inlet comprises a channel of a determined section and the gas valve comprises a valve body with a revolution surface rotatable in accordance with an axis intersecting the channel, which valve body is provided with a transverse channel which in an open position of the gas valve forms one continuous whole with the channel and wherein the fuel supply means comprise a vaporizer debauching into the transverse channel.
In the fully open position of the gas valve the intake air passes through the valve completely unimpeded, so that the cylinder can be filled with a maximum fuel/air mixture. During partial load the transverse channel of the valve body lies at an angle to the channel of the air inlet wherein edges of the valve body protrude in the channel of the air inlet. This results in very strong vortices which ensure good mixing of the injected fuel with the through-flowing air. This is of particular importance in the present invention because the fuel is continuously injected, while at lower rotation speeds the intake air flow has a pulsating component and the air speed is therein lower. Due to the specific embodiment of the gas valve very good mixing of the injected Fuel with the combustion air is also achieved under these conditions.
The pump is preferably a gear pump. This provides a very uniform output which is proportional to the rotation speed.
A suitable driving of the pump can be achieved with a direct current electric motor. The direct current electric motor can be controlled very precisely with per se known electronic control units.
A further development of the invention is characterized by moving the gas valve with a control motor which is regulated by the control device in accordance with the shaft rotation speed, the gas valve position and the position of a hand or foot-operated control member. Because the gas valve is not directly moved by the hand or foot-operated control member, it is possible through the control means to realize at all times an optimum adjustment of the gas valve for the momentary air flow and the momentary fuel flow rate and thus an optimal mixing of the fuel with the air. When full power is demanded from zero load and the control member is moved into the fully open position, a poor mixing of the fuel and air would occur in the case of a direct coupling because of the initially still low air speed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.